As it turns out, Justin Smith's upper body hasn't been feeling too good for much of the past 19 months.

The 49ers defensive tackle revealed Wednesday he spent the 2013 season playing with a shoulder injury he sustained in training camp. Smith didn't offer specifics, but acknowledged he knew the injury would require offseason surgery.

In December 2012, Smith sustained a torn triceps muscle, missed two games and played three postseason contests with a bulky arm brace before undergoing offseason surgery.

Last year's shoulder injury didn't noticeably slow Smith, 34, who earned his fifth straight Pro Bowl berth and ranked second on the team in sacks (6.5). However, he had 49 tackles, the lowest total of his 13-year career. Smith said the injury impeded his ability to shed blocks.

"You use your arms in football quite a bit (playing) inside," he said. "It was what it was. Moving forward. It feels good, so that's all that matters."

After having shoulder surgery, Smith was a spectator during offseason practices and it sounds as if he could reprise that role at times during training camp. The 49ers have a host of young backup defensive linemen, a group that includes Tank Carradine, 25, Quinton Dial, 24, and Tony Jerod-Eddie, 25.

"Training camp is more for getting down the feel of playing with guys and your assignments, the checks and stuff like that," Smith said. "I'm pretty confident with that and comfortable. I think it's a great opportunity for some of these young guys to get a lot of reps in training camp. I'm going to be playing in training camp, too. But let them get a lot of work."

Smith, who turns 35 in September, has two years remaining on his contract, but said he's only focused on this season. He chuckled when reminded that, in 2012, he thought he had three to four productive seasons left in him.

"I mean, I'm playing this year," Smith said. "That's my internal plan. I feel healthy compared to last year. I feel a lot better than I did last year. This is it. This is the one I'm thinking about and this is the one the team's thinking about. I'm not really concerned about next year."

Kaepernick on Sherman: Seahawks cornerback Richard Shermanrecently said he's "pretty much done" talking about Michael Crabtree, the 49ers wide receiver Sherman has said plenty about in the past.

Of course, "pretty much done" still gives Sherman a bit of wiggle room to continue lobbing shots at the man he's termed a "sorry" wideout.

"I think this team, and all of us, don't take the approach of talking about it," Kaepernick said. "We want to go out on the field and handle our business that way, go about it that way. We get to see 'em twice this year."

Injury updates: As expected, inside linebacker NaVorro Bowman(knee) was placed on the active/physically unable to perform list. Bowman is expected to start the regular season on the PUP list, which will require him to miss a minimum of six games.

The 49ers also placed tight end Garrett Celek on the PUP list. Celek participated in the offseason workout program and the nature of his injury is unknown.